By Oliver Holmes
BEIRUT (Reuters) - Syrian forces shot dead four civilians on a bus on Wednesday and fighting raged near Damascus, dissidents said, as international pressure mounted on President Bashar al-Assad to honor U.N.-backed ceasefire pledges to order his troops back to barracks.
In the city of Hama, an anti-Assad hotbed, an explosion ripped through a building, killing at least 12 people and wounding dozens more, according to the UK-based Syrian Observatory for Human Rights.
Another activist group, the grassroots Local Coordination Committee, said the blast was caused by a rocket launched into the building and put the death toll much higher at 54, including several children.
A third activist source said the explosion may have come from inside the building. It was not immediately possible to reconcile the varying accounts.
There was no comment from Syria's government, which says it is committed to U.N.-Arab League peace envoy Kofi Annan's April 12 ceasefire accord, but reserves the right to respond to what it says are continued attacks by "terrorist groups".
Hama has been hosting a small team of United Nations observers, who are preparing the way for a larger U.N. mission which will arrive to monitor the ceasefire pact.
In defiance of the truce accord, shelling was relentless in Douma, east of the capital, residents said, giving further ammunition to Western states such as France that want broad United Nations sanctions to try to end more than a year of fighting in which 9,000 people have been killed.
As well as urging faster deployment of U.N. monitors, French Foreign Minister Alain Juppe said Paris would push for a so-called "Chapter 7" resolution, which would mean punitive sanctions, next month if Assad's forces did not pull back.
"This cannot continue indefinitely. We want to see observers in sufficient numbers, at least 300 ... deployed as quickly as possible," Juppe said.
"If that does not work, we cannot allow the regime to defy us. We would have to move to a new stage with a Chapter 7 resolution at the United Nations to take a new step to stop this tragedy."
The Syrian Observatory for Human Rights said four people were killed when security forces opened fire on a bus at a checkpoint on the main road from Aleppo to Damascus.
An elderly man was also killed, it added, in heavy fighting in the southern city of Deraa, crucible of the anti-Assad revolt that flared 13 months ago after uprisings against autocratic leaders in North Africa and the Middle East.
A woman who visited Douma on Tuesday night said the town had been under constant shelling and was without water, power or mobile phone signal. Pro-government gunmen were wandering the streets, she added, preventing people from leaving their homes.
"There was bombardment all night. Artillery and tanks. We didn't sleep at all. Not for a moment," the woman told Reuters in neighboring Lebanon. "Most residents have gone down to live on the ground floor because most of the second and third floors have been hit."
There was no mention of the bus shooting or bombardment in Syria's rigidly controlled media or comment from the authorities in Damascus, which has barred most foreign journalists since the revolt started.
Annan, a former U.N. secretary-general, told the Security Council on Tuesday that Syria had failed to withdraw weapons from population centers in violation of the terms of the April 12 truce he engineered.
"Everything we have seen suggests that the Syrians are wanting to play for time and they haven't any real intention to start a political process and a transition. But we need to call their bluff, as it were, and test that," a senior Western diplomat told reporters in New York on condition of anonymity.
The latest violence comes two days after 31 people were killed in Hama immediately after U.N. monitors left the area and may prompt more outside pressure on Assad.
Damascus says 2,600 of its security personnel have been killed by the rebel armed groups that operate in parts of the country of 23 million.
"The situation in Syria continues to be unacceptable," Annan told the 15-nation Security Council. "The Syria authorities must implement their commitments in full and a cessation of violation in all its forms must be respected by all parties."
He stressed the need to get "eyes and ears on the ground", but peacekeeping chief Herve Ladsous said it would take a month to deploy the first 100 monitors of the UNSMIS mission - a time frame that drew derision from ordinary Syrians.
"It takes them a month to arrive? Are they coming on horses?" asked a resident of Homs, a city which has endured constant army shelling. He declined to give his real name.
The reasons for the slow deployment were not clear, although diplomats said Norwegian General Robert Mood, who led a U.N. negotiating team to Syria this month, had been made its head.
So far, there are only 15 unarmed monitors in Syria out of a planned final team of 300, a frustratingly thin presence for the opposition activists who say they have noted some decline in the daily death toll.
In a display of Syrian black humor, some activists have mocked the monitors, appearing on video in spoof blue uniforms and with blacked-out glasses and tissue paper stuffed into their ears - pretending neither to see nor hear anything untoward.
"After one month we will have maybe 1,000 or 2,000 people killed - it's ridiculous. How can the international community watch without moving quickly?" asked Mousab al-Hamadi, an opposition resident in Hama province, a hotbed of the revolt.
Annan said Syrian Foreign Minister Walid al-Moualem had written to him saying that "the withdrawal of massed troops and heavy weapons from in and around population centers is now complete and military operations have ceased".
However, Annan's team cited satellite imagery as evidence that tanks are lurking out of sight on the outskirts of cities. Even Syria's ally Russia voiced concern.
Russia's U.N. ambassador, Vitaly Churkin, said it would be worrying if Damascus had failed to withdraw troops and weapons.
"If this is the case, if the promise in the letter has not really been carried out, that would mean it is a breach of the promise they made on Saturday," Churkin said. "I'm certainly going to bring it to the attention of Moscow."
Throughout the conflict, Russia has been one of Assad's few friends, providing protection at the United Nations from any Security Council measures.
For all the rhetoric, France and other Western powers have few tools to dislodge Assad, who succeeded his long-ruling father Hafez al-Assad in 2000 and who has brushed aside all calls to hand over power.
They are particularly wary of military intervention similar to NATO's Libya air campaign that helped topple Muammar Gaddafi for fear it could draw in powerful Assad allies such as Iran and Hezbollah militants and further destabilize the Middle East.
(Additional reporting by John Irish, Louis Charbonneau and Dominic Evans; Writing by Ed Cropley; Editing by Alistair Lyon/Mark Heinrich)